The Vivaldi tapered notch, or horn, is printed on films of Kapton or other very thin dielectric. Printing is accomplished by standard printed circuit techniques whereby the Kapton material is coated with copper or other conductor. The horn and the feed network, including waveguides and impedance matching slot line baluns are produced by photo-etching. Since most of the copper remains on the dielectric film, it contributes to the stiffness of the device without which the device would not be self-supporting, and it provides a heat dissipation path and significant radiating area for thermal control of the T/R modules.
Briefly stated, the invention provides a radiating tapered notch antenna (sometimes known as a Vivaldi antenna) which is fed by a section of slotline, which in turn is fed by a coplanar waveguide. The transition from the unbalanced coplanar waveguide to the balanced slotline is accomplished by an infinite balun, where the center conductor of the coplanar waveguide terminates on the slotline conductor opposite the ground conductor of the coplanar waveguide. One slot of the coplanar waveguide becomes the feeding slotline for the notch, and the other slot terminates in a slotline open circuit. All of the elements of the system are coplanar.
U.S. Pat. No. 4,853,704 issued on Aug. 1, 1989 to Diaz et al, discloses a tapered notch, printed circuit antenna assembly having a strip conductor, and a ground plane separated from and lying parallel to the strip conductor. The ground plane has a slot which extends transverse to the strip conductor. The antenna comprises a conductive planar element positioned across the slot and orthogonal to the ground plane, and has curved surfaces extending upward and outwardly from the slot. The strip conductor or microstrip and the slot-containing ground plane are separated by a dielectric material. This invention is an improvement over Diaz in that the ground plane is eliminated, and in that all of the components are coplanar.
In designing an antenna for radio frequency energy it is important that the antenna be compatible with the feeding network, that is, the transitional device that is to be employed between the antenna element and the feed means to excite the element should be one with little or no discontinuity that would cause bandwidth restrictions.
In seeking a broadband antenna compatible with a feed network, light in weight, rugged in construction and yet simple to construct, the choices available to an antenna engineer are rather limited. In designing an antenna along with any necessary impedance-matching or power-dividing circuit component associated therewith, an antenna designer must make the antenna perform a desired electrical function which includes, among other things, transmitting/receiving linearly polarized, right-hand circularly polarized, left-hand circularly polarized, etc., R. F. signals with appropriate gain, bandwidth, beam width, minor lobe level, radiation efficiency, aperture efficiency, receiving cross section, radiation resistance as well as other electrical characteristics.
It is advantageous for an antenna structure to be lightweight, simple in design, and inexpensive. The Vivaldi, or tapered notch antenna, is advantageous since it can be constructed by simple photo-etching techniques well-known in the art. Such techniques offer ease of fabrication at a relatively low production cost. Briefly, the tapered notch antenna is formed by etching a single side of a unitary metal clad dielectric sheet or electrodeposited film using conventional photoresist-etching techniques. Typically, the entire antenna structure may possibly be only 1/32 inch to 1/8 inch thick which minimizes cost and maximizes manufacturing/operating reliability and reproducibility.
It can be appreciated that the cost of fabrication of such printed circuit board antennas is substantially minimized since single antenna elements and/or arrays of such elements together with appropriate R. F. feed lines, phase shifting circuits and/or impedance matching networks may all be manufactured as one integrally formed electrical circuit by using low cost photoresist-etching processes commonly used to make electronic printed circuit boards.